1. The Link Between Underluminous Supernovae Explosions, Gravitational Waves and Extremely Low Mass White Dwarfs
Alex Gianninas
Mukremin Kilic, Warren Brown, & J.J. Hermes
December 9th, 2013
27th Texas Symposium

2. White Dwarf Properties
M ~ 0.6 M
R ~ 0.01 R ~ 1 R
 ~ 106 
log g ~ 8.0
(log g = 4.4)
Teff ~ 150,000 
3000 K
No H burning  WDs cool over several Gyrs
12/2/2019
Texas Symposium

3. Gianninas et al. (2011)
Binary Evolution
12/2/2019
Texas Symposium

4. Many will merge in less than a Hubble time!
These “friends” are binary companions that stripped a significant amount of material from the progenitor, preventing the ignition of He burning, giving birth to an extremely low mass (ELM) WD
ELM WDs are found almost exclusively in short-period binaries (P < 1 day)
Many will merge in less than a Hubble time!
12/2/2019
Texas Symposium

5. ELM Survey Targeted search for Extremely Low Mass WDs
ELM WDs = M < 0.25 M
Motivation:
Progenitors of Type Ia supernovae (DD channel)
Progenitors of underluminous supernovae
(.Ia SN; Bildsten et al. 2007)
Progenitors of AM CVn systems (Kilic et al., 2013)
Pulsar companions
(e.g. PSR J ; Kaplan et al. 2013)
Nearest systems are important sources of gravitational waves!
12/2/2019
Texas Symposium

6. ELM Survey: Target Selection
Hypervelocity Survey (Warren Brown, SAO): search for B type stars leaving the Galaxy, colors similar to ELM WDs  15% of targets are in fact ELM WDs
Spectroscopy from the Sloan Digital Sky Survey (SDSS)
SDSS colors (u-g, g-r)
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Texas Symposium

7. ELM Survey: Target Selection
Brown et al. (2012)
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Texas Symposium

8. ELM Survey: Follow-up MMT (6.5m), FLWO (1.5m), KPNO 4m
Radial velocity follow-up to confirm the binary nature of each candidate
Once confirmed, we seek to improve our orbital solution by better sampling all phases of the orbit
12/2/2019
Texas Symposium

9. ELM Survey: Success Rate
Paper
ELM WD
Merger Systems
Brown et al. (2010) I 12 6
Kilic et al. (2011) II 4 2
Brown et al. (2012)
III 7
Kilic et al. (2012) IV 5
Brown et al. (2013) V 17
Before ELM Survey:
Only 6 known merger systems (SPY)
Shortest known period is P = 1.5 hr
ELM Survey has found 8 systems with P < 1.5 hr and 3 with P < 1 hr
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10. Orbital solutions provide period (P) and velocity semi-amplitude (K)
Brown et al. (2013)
Orbital solutions provide period (P) and velocity semi-amplitude (K)
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Texas Symposium

11. ELM Survey: Results
Super-Chandrasekhar mass systems not necessarily Type Ia progenitors
Mass ratio is important
M systems → Stable mass transfer system (AM CVn, .Ia SN)
Can be WD+NS binaries
Brown et al. (2013)
12/2/2019
Texas Symposium

12. Progenitors of AM CVn (cataclysmic variables, novae)
Massive Companion
Pulsars? No detections with Chandra
Will undergo stable mass transfer
Result: AM CVn
Kilic et al. (2013)
12/2/2019
Texas Symposium

13. Masses & Radii Model dependent and model independent measurements
Eclipses
Ellipsoidal variations (tidal distortion)
Model dependent: two ingredients
Precise measurements of the atmospheric parameters (Teff and log g)
Evolutionary models (Althaus et al., 2013)
12/2/2019
Texas Symposium

14. Gravitational Wave Strain
Gianninas et al. (2014, in prep)
Galactic foreground
LISA, 1yr, S/N = 5
LISA, 1yr, S/N = 1
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15. eLISA
Replaces LISA
Two beams instead of three
Reduced sensitivity
Frequency range spans four decades (~0.1 mHz – ~1 Hz)
“The Gravitational Universe” approved as science theme for ESA L3 project ( launch in ~2034)
12/2/2019
Texas Symposium

16. eLISA Verification Sources
Amaro-Seoane et al. (2013)
12/2/2019
Texas Symposium

17. J0651 ‘‘Poster child” for ELM WDs
Shortest period ELM WD binary  P = min!
Eclipsing!
After initial discovery, photometric follow-up at McDonald, APO, Gemini North and GTC
Hermes et al. (2013)
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Texas Symposium

18. Direct detection of orbital decay!
Light Curves for J0651
Direct detection of orbital decay!
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Texas Symposium
Hermes et al. (2013)

19. O-C Diagram for J0651
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Texas Symposium
Hermes et al. (2013)

20. Hulse-Taylor Pulsar PSR B1913+16
30 YEARS!
Weisberg & Taylor (2005)
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21. Conclusions ELM Survey: targeted search for extremely low-mass WDs
Success: ~60 systems with P < 1 day
J0651
Rate of orbital decay agrees with GR
Only takes a few years to detect
Verification source for eLISA
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Texas Symposium

22. More to come… ELM Survey J0651
Ongoing: upcoming observing runs on MMT and KPNO 4m
Expand to Southern Hemisphere
NEW! : 20-min system discovered!
J0651
Continued monitoring
12/2/2019
Texas Symposium